1. Field of the Invention
This invention relates to a valve-actuating mechanism for a three-valve internal-combustion engine.
2. Description of the Prior Art
The inner surface of each cylinder head of a known three-valve internal combustion engine is provided with a combustion chamber facing the upper surface of a piston fitted slidably in the cylinder. The roof surface of the combustion chamber is provided with two suction valves and one exhaust valve. Such an internal-combustion engine has a high suction efficiency, and is capable of providing a high output. However it has a large number of valves for each cylinder, which means that the cost of manufacturing the engine increases. Additionally, the load on the cam shaft actuating these valves is high. A high load on a cam shaft can cause deflections thereof, and the timing of the operations of the valves is often disrupted slightly. In order to prevent such problems, it is necessary to increase the rigidity of the cam shaft, but this results in an increase in the weight of the engine as a whole.